Abstract
In vitro propagation of olive (Olea euorpea L.) always remained a challenging task due to its woody nature and oxidation of culture. The current study intended to optimize shoot induction and proliferation protocol for different cultivars ("Leccino", "Gemlik", "Moraiolo" and "Arbosana") of olive-on-olive media (OM) provided with different concentrations (0, 0.5, 1.5, and 2.5 mgL(-1)) of 6-benzylaminopurine (BAP) by pre-exposing their explants (nodal segments) with different regimes (0, 24, and 48 h) of cooling. The impacts of treatments were evaluated on morphological (shoot induction percentage, primary shoot length, number of leaves shoot(-1), and number of shoots per explant(-1)), physiological (total chlorophyll, carotenoids, CO2 assimilation, and proline), biochemical (primary and secondary metabolites) attributes of cultivars after 50 to 60 days of culture. Data recorded were subjected to statistical analysis. All traits depicted significant increases in all genotypes with increasing pre-cooling treatments and increasing supplementations of 6-benzylaminopurine (BAP). This increase was the highest for the interaction of 48 h pre-cooling and 2.5 mgL(-1) BAP concentration. Moreover, correlation analysis of all traits revealed significant paired association among them in a positive direction, while principal component analysis (PCA) revealed the extent of association varied with types of treatments and the nature of genotypes. Among cultivars, Arbosana depicted more dramatic changes in morphological traits, physiological attributes, and biochemical contents due to varying interactions of pre-cooling and BAP treatments as compared to Moraiolo, Gemlik, and Leccino with in vitro systems.